1) Field of the Invention
The present invention relates generally to agricultural implements and, more specifically, to a spring trip standard for tillage implements.
2) Related Art
Spring trip standards typically include a mounting bracket attached to rectangular toolbar and extending upwardly and rearwardly to a downwardly and forwardly directed spring abutment surface. A spring is compressed between the abutment surface and an upwardly directed spring abutment surface on a member pivotally connected to the lower portion of the bracket, and a tool supporting shank is fixed to the member. A tension link assembly extends from the shank supporting member through the spring and through an aperture in the spring abutment surface on the bracket to adjust the preloading of the spring and vary the vertical position of the tool connected to the shank. Such an assembly is shown by way of example in U.S. Pat. No. 3,700,039 entitled SPRING TRIP SHANK ASSEMBLY. This type of shank assembly provides good trip force characteristics but has numerous parts and is expensive and time-consuming to assemble and repair. Previously available assemblies, particularly those with numerous tension link or spring support components such as pins, straps, spacers and washers, typically require extensive instructions for assembly and disassembly.
In some shank assemblies, the tension link reduces forces on the pivot area in the at rest position, thereby introducing some looseness in the pivot joints which often is perceived as a quality disadvantage and which causes the tool to have some lateral shift during operation. Often the precompression of the spring when the tool is in the normal operating position is not sufficient to prevent some continual tripping action. The portion of the tension link extending through the aperture is subject to wear as a result of such tripping action. In spring trip shank assemblies of the type shown in U.S. Pat. No. 4,520,878 the bottom of the coil spring rests on a seat which can swivel to maintain the lower face of the spring substantially normal to the longitudinal axis of the spring and thereby reduce spring buckling forces. In another type of assembly shown in U.S. Pat. No. 3,700,039, the lower end of the coil spring is free to rock on a clamp bolt to remain normal to the centerline of the spring. These devices introduce additional wear components into the assembly.
In our commonly assigned and copending application Ser. No. 09/216,270 filed Dec. 18, 1998 and entitled SPRING TRIP STANDARD, we describe a spring trip arrangement which does not require a tension link. In commonly assigned application Ser. No. 09/325,454 filed Jun. 3, 1999 and entitled SPRING TRIP STANDARD HAVING REDUCED SPRING BUCKLING FORCES, spring seat structure is described for providing generally perpendicular alignment of the lowermost coil of the spring relative to the centerline of the coil spring in both the field-working and the tripped positions so that spring buckling and spring fatigue caused by buckling are reduced. Upstop limit for the shank is provided by the spring when the spring coils stack against each other. When a shank trips upwardly over a large obstacle to the maximum tripped position, the force can be so great on the fully compressed spring, even when properly aligned between the spring abutment surfaces on the assembly, that the spring coils slip past one another causing permanent deformation of the spring and loss of normal spring characteristics.